A number of Muslim scholars believe that Prophets do not sin. Others accept it based on the Quran that they do, but they are "minor" sins only. These in general are treated as mistakes. Those who do not beleive that Mohammad sinned, is not based on the teachings of the Quran, but based on two fundamental reasons outside of the Quran. One is that Jesus is the only one in the Quran is said to be "blameless". This results in embrassement for some Muslims, as Mohammad is asked to ask for forgiveness. Two, if Mohammad or any of the Prophets were sinners, than how can we have a "pure" revelation from God. Coming through "impure" and "sinful" Prophets would result in these being corrupted. Those who accept that Prophets commit minor sin, do so, but not in the matter of receiving relevation.

Sunni Muslim translators of the Quran use differeing approaches to the issue of Sin of the Prophets. Notice how Shakir uses the word "fault" and not "sin". In my opinion, of the three translators that are commonly used by Sunni Muslim - Yusuf Ali, Shakir and Pickthal, Pickthal is generally more "literal", while Shakir is the one who is "interpretive" and Yusuf Ali is in the middle.

Note how this ayat is tranlated. Yusuf Ali uses the word "sin" while Shakir use "fault".

(Their plight will be) no better than that of the people of Pharaoh, and their predecessors: They denied our Signs, and God called them to account for their sins. For God is strict in punishment. Yusuf Ali, Quran 3:11

Like the striving of the people of Firon and those before them; they rejected Our communications, so Allah destroyed them on account of their faults; and Allah is severe in requiting (evil). Shakir, Quran 3:11

Now when we come to the Sins of Mohammad, even Yusuf Ali is "interpretive". He now translates the same arabic word "dhanb" above as "sin", but below as "faults" while Pickthal is consistent in treating it as "sin".

That God may forgive thee thy faults of the past and those to follow; fulfil His favour to thee; and guide thee on the Straight Way; Yusuf Al, Quran 48:2

That Allah may forgive thee of thy sin that which is past and that which is to come, and may perfect His favour unto thee, and may guide thee on a right path, Pickthall, Quran 48:2